"Valley of Tears" visits a Mexican-American community that works the onion fields of rural south Texas in three different eras, observing how the seeds of change planted 20 years ago seem ready to bear fruit today.

The little town of Raymondville, Texas, is not precisely in President Bush's backyard, but by Texas standards, I suppose, it's close enough. And by cultural standards, the life of this little onion patch near the Rio Grande  which jokingly calls itself "The Breath of a Nation"  is a little piece of America at its most troubling.

For most of a century  as we learn in this documentary by Hart Perry ("Harlan County U.S.A.")  Raymondville has been two towns in one, separate and unequal. White citizens in prim houses own the fields; Mexican immigrants pick the onions in them. It's been that way for most of a century, and anyone who would question the order of things is obviously some kind of subversive.

In fact, when first we see the town, the traditional labor peace is being stirred up by what the whites dismiss as "agitators" from the United Farm Workers. The first of the film's three segments features archival footage from a late-1970s strike among Mexican-American onion pickers at peak harvest time. The local authorities are arrayed on the side of the white planters, of course, and the officers' crackdowns against the strikers, because they're caught on film, make a vivid reminder of the way labor battles has traditionally been kept in line for 150 years. When strikers protest that they need a little protection, they're told, "You're dealing with a different kind of law."

The second segment of the film shows the chicano population's campaign to get representation on the local school board for the first time. With children pulled out of school to work in the fields for several months a year, many perform badly and drop out, and the community wants changes that will help its kids graduate.

The third segment jumps forward to the 1990s and profiles a member of the Mexican-American community who was one of these kids discouraged from pursuing an education. Through perseverance, he has gone to college and law school and run for district attorney.

"Valley of Tears" never feels very thorough but it is well worth seeing for the clues it presents to the state of race relations from the 1970s to the present  especially in out-of-the-way locales like rural Texas where, in the absence of a documentary film crew, the outside world will never see what happens. This is the hidden world of the civil-rights struggle. (In a fictional setting, John Sayles' "Lone Star" was about exactly the same transformation we can observe here.) Gradually, we see Mexican-American families begin to challenge the total subjugation they experienced for decades, and the beginnings of Latino self-governance. We are the majority, they often remind themselves, and the town's dominant white culture is just beginning to reluctantly give way in the film's later scenes.

If you sympathize with the Mexican-Americans on the screen, it's still a film full of failures and silver linings. Workers are outmaneuvered by local agribusiness but they still feel they've made a change if only in their own minds. Students continue to fail out of high school, but there are some success stories  and maybe those talented sons and daughters will make a difference in future years. One candidate stands up and challenges the political establishment, never gaining the confidence of the anglo population, but it's a beginning toward remaking the town on fairer terms. Many of the victories are moral ones  call it a story of empowerment. It's a term that sounds almost trite today, but the idea of empowerment is given quite concrete meaning in this movie. By the end, the people we see have a sense that they have a hand in their own destinies, which is more than they had in the film's opening minutes.